Researchers interested in the evolution of animal genitalia tend to focus on the male side of that equation, often unjustifiably ignoring the female

Penises are amazingly diverse things. They can be long or short, thick or thin, arrow-straight or oddly curved. As a result, researchers focus a lot of attention on these intriguing organs, often dismissing female genitalia as simple, boring receptacles.

As a generally penis-obsessed species, you might assume we were talking about human sexual organs. But guess again. Biases towards the male organ—and against vaginas and other female genitalia—permeate the biological literature and research community. In other words, we love all things penis so much that we invest an inordinate amount of attention on studying animal penises, too. Sometimes, we want penis so badly that we are quick to declare that out-of-the-ordinary female animal genitalia is actually just a penis.

To reveal our inclination toward the phallic, researchers from Europe and Australia performed a meta-analysis of all research papers published between 1989 and 2013 that focused on the evolution of genitalia. As they reported in PLoS Biology, they found 364 such studies, which they combed through to quantify the amount of attention the authors devoted to male genitalia only, female genitalia only or just general genitalia with no preference one way or the other. They controlled for factors such as whether the paper needed to focus on one gender to answer a specific research question.

Male genitalia, they found, greatly dominated the literature. Surprisingly, this tendency has increased over the past ten years. In the last decade, half of all studies on genital evolution focused solely on males, while less than ten percent were devoted to females.

The authors didn’t stop there, however. They wanted to tease out the reasons behind this bias. Giving the scientists the benefit of the doubt, they decided to see whether or not researchers are just swayed in favor of the easier-to-access genitalia. In other words, maybe penises get more study simply because they conveniently stick out, compared to vaginas and other female organs that are concealed within the body.

However, as biologists well know, not all species possess protruding penises. Reptiles, birds and insects, for example, often require some digging to get at those male organs. When the authors controlled for this, they found that ease of accessibility did not explain why so many researchers chose to focus on penises and other forms of male genitalia.

Continuing their hunt for an explanation, the authors wondered if female genitalia really are just kind of boring. If vaginas possess little variation between species, then maybe they warrant less attention. On closer inspection, however, they found that those studies that did bother to focus on vaginas revealed a tremendous diversity of variation, not just between different types of animals but even among individual females of the same species.

Female waterfowl, for example, have elaborate genitalia that—like an internal labyrinth—can include several dead-end vaginal sacs, likely for preventing rapey males from actually siring their ducklings. Clearly, there is nothing boring or simple about those vaginas.

Finally, the researchers analyzed whether or not the gender of the lead authors of those studies might be influencing the research question. Men—stereotypically penis-obsessed—might be driving the literature toward examination of those organs. But gender bias didn’t explain it, either. Both male and female authors were equally prone to focusing on the phallic and ignoring the feminine.

Faced with no other plausible explanation, the authors of the new study concluded that people—even highly educated biologists—are “increasingly and unjustifiably biased toward the study of male genitalia,” the write. “The bias reflects enduring assumptions about the dominant role of males in sex, and invariant female genitalia.”

Needless to say, these assumptions, they point out, are flawed, especially in light of recent research showing, for example, that female genitalia can rapidly evolve on its own, and that males and females are locked into a complex, intrinsically linked co-evolution of sex organs.

Simply focusing on one gender and ignoring the other provides only half a picture, the authors note. Not only do such one-sided studies risk misinterpreting the findings, the authors write, but they also miss out on the “extremely rich” evolutionary dynamics that so often play out between the sexes. After all, it does take two to tango.

As this female chimp attests, lady parts can be just as interesting as male ones. Photo: Frans Lanting/Corbis

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About Rachel Nuwer

Rachel Nuwer writes for Smart News and is a contributing writer in science for Smithsonian.com. She is a freelance science writer based in Brooklyn.

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